I'm also aware of how iMessages and SMS are used in the US, yet this is very US-specific, and I don't believe any other country uses SMS.
For Chinese people, WeChat is the standard, and what pretty much anyone uses.
In Argentina and the Netherlands (and I believe much of the EU), WhatsApp is ubiquitous.
Yet, I don't know a single person who uses either SMS or Messenger, or iMessages.
So what truly fascinates me, is how different companies put so much work into developing such sophisticated messaging apps, but they're all reinventing the wheel and each consumed in different regions -- I think nobody would have guesses years ago that we'd have so many different apps used in different countries, and not at all inter-operating with each other.